SGEM#156: Working at the Abscess Wash – Irrigation of Cutaneous Abscesses?

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Date: May 25th, 2016

Guest Skeptic: Chip Lange is an emergency medicine Physician Assistant (PA) working primarily in rural Missouri community hospitals. He has international experience in critical care and emergency medicine. Currently, he is working on developing a new blog and podcast specifically for PAs in emergency medicine but wants all those who take care of critically ill or injured patients to be able to learn.

Case: A 30-year-old female with a history of cutaneous abscesses comes to your emergency department stating she thinks she has another one developing on her arm. She tells you she wants to do as little as possible to treat the abscess using an incision and drainage because she hates the pain from the procedure, especially the irrigation.

Background: Cutaneous abscesses are a very common complaint in the emergency department and there is much debate about the management of abscesses. The mainstay management of an abscess is incision and drainage. Other management may include wound culture and sensitivity, pain control, packing and antibiotics.

There is lots of dogma around wound care and we have covered some of these issues before on the SGEM (Dogma of Wound Care). With regards to abscesses we have discuss packing or not packing. Our bottom line in 2012 was that routine packing of simple cutaneous abscesses might not be necessary (Better Out than In).

Another issue that has been debated is whether or not to routinely prescribe antibiotics. A study by Hankin and Everett. Are Antibiotics Necessary After Incision and Drainage of a Cutaneous Abscess? was published in Ann Emerg Med 2007. We reviewed this paper on SGEM#13. Our conclusion at that time was that the evidence did not support using antibiotics routinely in simple cutaneous abscesses even in the era of MRSA.

A new study looking at Trimethoprim–Sulfamethoxazole versus Placebo for Uncomplicated Skin Abscess by Talan et al was published in NEJM March 2016. We will be reviewing this study soon on the SGEM.

Apparently there is no randomized controlled trial demonstrating the benefit of irrigation in the treatment of simple cutaneous abscesses. Treating these conditions can be painful, takes time and has a financial cost.There is also the risk of contamination to the patient and emergency medicine provider, like the PA doing the irrigation.

Clinical Question: Does irrigation of a cutaneous abscess after incision and drainage reduce the need for further intervention?

Reference: Chinnock and Hendey. Irrigation of Cutaneous Abscesses Does Not Improve Treatment Success. Ann Emerg Med 2016.

Population: Emergency department patients >18 years old with a cutaneous abscess
- Excluded: Pregnant, police custody, prison resident, admitted to hospital, taken to the OR, inability to follow-up in 48hrs or to provide contact information for 30-day follow-up.
Intervention: Incision and drainage plus irrigation
Comparison: Incision and drainage alone
Outcome: Need for further intervention in the next 30 days after the initial incision and drainage (Interventions include: repeat incision and drainage, antibiotic change, or abscess related hospital admission within the next 30 days).

Author’s Conclusions: “Although there were baseline differences between groups, irrigation of the abscess cavity during incision and drainage did not decrease the need for further intervention.”

Quality Checklist for Randomized Clinical Trials:

The study population included or focused on those in the ED. Yes
The patients were adequately randomized. Yes
The randomization process was concealed. Yes
The patients were analyzed in the groups to which they were randomized. Yes
The study patients were recruited consecutively (i.e. no selection bias). No They state that enrollment was “sporadic and non-consecutive” with most patients eligible not being enrolled.
The patients in both groups were similar with respect to prognostic factors. Unsure
All participants (patients, clinicians, outcome assessors) were unaware of group allocation. No. The randomization was blinded but after group allocation patients and clinicians knew what group they were in.
All groups were treated equally except for the intervention. No. The irrigation group received more packing and antibiotics.
Follow-up was complete (i.e. at least 80% for both groups). Yes
All patient-important outcomes were considered. Yes
The treatment effect was large enough and precise enough to be clinically significant. No

Key Results: Two hundred and nine patients were enrolled with 187 completing the study. The median age was in the late 30’s with just over 40% being female.

No difference in need for further intervention at 30 days

Primary Outcome: 15% irrigation group vs. 13% in the non-irrigation group. There was a 2% non-significant difference (95% CI -8% to 12%)
Differences Between Groups: Irrigation group was about 5 year younger, had packing more often (89% vs. 75%) and received outpatient antibiotics more often (91% vs. 73%).

Single Centre: This was a single center study with a high rate of MRSA, which can limit its generalizability to other practice settings.
Not Consecutive: Patients were not recruited consecutively but rather sporadically and most eligible patients were not enrolled. This could have introduced some selection bias into the study. They state; “However, we do not believe the results were biased because patient were enrolled on all days of the week, both day and night.”
Unbalanced groups: The groups were not balanced at baseline with the irrigation group being five years younger. While statistically significant it is probably not a clinically important difference.
Treated Differently: The two groups were not treated equally. The irrigation group was more likely to have packing and receive antibiotics. There is evidence suggesting packing does not make a difference, although it is relatively weak. The issue of outpatient antibiotics after incision and drainage is even more complicated given the recent study by Talan et al. However, that should have biased the study towards irrigation being superior but the key result was no statistical difference. Another problem was the lack of standardization in the irrigation solution used or the amount of irrigation.
Non-Blinded: Patients and clinicians knew the group allocation. This could potentially explain some of the variation in treatment observed between the two groups. The lack of blinding and differences in treatment make it more difficult to interpret the results.

Comment on Authors’ Conclusion Compared to SGEM Conclusion: We agree with the author that based on this data that irrigation does not appear to improve outcomes after incision and drainage of cutaneous abscesses. However, the study does have significant limitations and a future study with standardized treatment protocols would help clarify whether irrigation provides any efficacy.

SGEM Bottom Line: Irrigation of a cutaneous abscess after an initial incision and drainage is probably not necessary.

Case Resolution: You discuss with your patient that there is some evidence suggesting that irrigation does not appear to improve outcomes versus not doing the irrigation. With shared decision-making, you decide not to irrigate the abscess.

Clinical Application: Although abscess management varies by location and patient, irrigation of simple cutaneous abscesses may not be needed, as it does not seem to improve treatment success.

What Do I Tell My Patient? We know that incision and drainage can be painful and we want to reduce that pain as much as possible. There is new evidence that suggests irrigation of your abscess may not be beneficial and we can skip this painful part of the procedure if you would like.

Keener Contest: Last weeks’ winner was Shawn Murphy a Physician Assistant from Parry Sound, Ontario. He knew that appendicitis can present at any age and the youngest person to have an appendectomy, according to the Guinness Book of World Records was Sebastian Perez at 9 days old.
Listen to the podcast for this weeks’ question. If you think you know the answer, email TheSGEM@gmail.com with keener in the subject line. The first correct answer will receive a cool skeptical prize.